Direct Torque Control of Induction Motor with Stator Flux Estimation Based on an Improved Voltage Model

Abstract

Using sensors to measure the stator flux for induction motor presents many drawbacks such as far less reliability, noisy signals, vibration, and additional cost. Thus, it is essential to synthesize an estimator (also called a software sensor) allowing to replace the hardware sensor, for the flux estimation. In general, this estimation is done by integrating the back electromotive force (EMF) of the stator. However, the presence of the pure integrator presents problems due to the inevitable DC component and the initial condition error in the back EMF. To overcome these problems, a low pass filter has been used in the literature. Nevertheless, this solution does not solve the problem of undesirable high-frequency noise, especially at low speed. In this paper, we present a solution to improve the stator flux estimator by proposing a fractional or- der integrator to estimate the flux at low speed. This solution does not require any hardware device; it involves low calculation time and provides accurate practical results. The proposed solution has been implemented using the dSPACE 1104 platform.